The present invention relates to a process for preparing pellets of hydrolyzed ethylene-vinyl acetate copolymers, and more particularly to a process for preparing pellets of hydrolyzed ethylene-vinyl acetate copolymers having an improved melt-moldability and capable of giving films having improved physical properties.
Hydrolyzed ethylene-vinyl acetate copolymers are widely employed for various uses such as films, sheets, containers and fibers since the hydrolyzed copolymers are excellent in properties such as oxygen-barrier property and mechanical strength. In these uses, hydrolyzed ethylene-vinyl acetate copolymers are melt-molded. In the melt-molding, the flow of the hydrolyzed copolymers is bad in a portion contacting a wall of a mold since hydrolyzed copolymers have a large adhesion to metals in the melted state. When the melt-molding is continued for a long time, it is impossible to operate stably or to increase the productivity by increasing extrusion rate since the screw torque increases. Accordingly, when the hydrolyzed copolymers are melt-molded for a long time, generally, copolymers are blended with lubricants in a small amount.
When molded articles such as sheets or films are prepared by melt-molding, hydrolyzed ethylene-vinyl acetate copolymers must be formed into pellets from the point of handling or molding processability, and it is general that the hydrolyzed copolymers are dry-blended with the lubricants and the mixtures are supplied to an extruder to form into pellets.
However, the addition of lubricants is never preferable from the point of properties of molded articles such as films. For instance, bleeding of lubricant occurs due to the lack of compatibility between hydrolyzed ethylene-vinyl acetate copolymers and lubricants. As a result, the adhesive strength to other materials decreases in the case of laminating or coating the hydrolyzed copolymers on the materials, or fish eyes are formed on the surface of the molded articles such as films and sheets.
Accordingly, in the conventional method, it is substantially impossible that the molding processability is improved without damaging properties of the molded articles.
An object of the present invention is to provide a process for preparing pellets of hydrolyzed ethylene vinyl acetate copolymers having an improved molding processability.
An another object of the present invention is to provide a process for preparing pellets of hydrolyzed ethylene-vinyl acetate copolymers capable of giving molded articles having improved properties.
These and other objects of the present invention will become apparent from the description hereinafter.